CN109414961B - Tyre comprising a tread comprising reinforcing elements - Google Patents

Abstract

The present invention discloses a tire, the tread of which comprises a tread base layer and a circumferential reinforcement composed of a rubber compound having a stiffness greater than that of the rubber compound and the tread base layer. The tire has an outer side and an inner side, and the circumferential reinforcement includes tapered reinforcing elements in tread rib elements that are axially located in the first circumferential direction of the tread when viewed from the outer side to the inner side Outside of the groove or the second circumferential groove, and axially close to said circumferential groove.

Description

Tires including treads containing reinforcing elements

technical field

The present invention relates to tires, and more particularly to tires having improved grip properties.

Background technique

As is well known, whether tires are intended to be mounted on passenger vehicles or heavy-duty vehicles, the tread of the tire is provided with a tread pattern consisting in particular of various main, longitudinal or circumferential, transverse or inclined grooves Defined tread pattern elements or basic blocks, which can also have various finer slits or grooves. The grooves form channels for water drainage during running on wet ground, and the walls of these grooves define the leading and trailing edges of the tread pattern elements, depending on the direction of curvature.

In order to improve the grip of a tire, and more particularly on dry and wet surfaces, it is known to reduce the stiffness (or stiffness or hardness) of the rubber compound that makes up the tread. This reduction in tread stiffness allows the tread to better match the rough surface of the running surface, so the actual contact area with the running surface is increased, and grip performance is improved relative to a tread with a harder rubber compound.

However, especially in the case of lateral grip, the use of a less rigid rubber tread compound promotes the shearing of the tread element and its vibrations, and this produces a greatly elevated on the leading edge of the tread element pressure, which in turn generates very significant heat.

These elevated pressures and this heat can lead to very rapid damage to the tire tread and suboptimal utilization of the potential grip of the tread rubber compound.

In order to improve the performance of tires with grooves by stabilizing the tread pattern elements, document EP 2 708 382 A1 proposes a tire having in its tread a circumferential reinforcement made of a rubber compound, said rubber The stiffness of the compound is greater than that of the rubber compound of the rest of the tread, and said circumferential reinforcing elements are located below each circumferential groove and extend radially from the radially inner surface of the tread until it forms the entire bottom of the groove.

Another example is given in the document JP H08 342015.

The resulting reinforcement of the circumferential grooves makes it possible to increase the drift thrust of the tire, but the presence of a rigid compound in the groove bottom makes it difficult to mold wear indicators. A significant increase in rolling resistance was also observed, particularly in relation to the limitation of the lateral and longitudinal flattening process.

SUMMARY OF THE INVENTION

The subject of the invention is a tire having an axis of rotation and a median plane perpendicular to the axis of rotation, and comprising a crown with a crown reinforcement, a tread located radially outside, said tread comprising a plurality of tires A tread pattern element having a side surface and a contact surface intended to be in contact with the road surface when the tire is driven, a plurality of circumferential grooves, each circumferential groove being formed by an outer side surface of an opposing adjacent tread pattern element and the inner side, and bounded by the bottom, the circumferential reinforcement, which is made of a rubber compound, the stiffness of which is greater than the stiffness of the rubber compound of the rest of the tread, and the bottom layer, which is arranged radially towards the inner side And radially on the outside of the crown reinforcement, characterized in that the tire has an outside and an inside, and the circumferential reinforcement has reinforcing elements, which are arranged relative to the tread from the outside to the inside. In a tread pattern element in which one of the first circumferential groove and the second circumferential groove is arranged axially on the outside and is axially close to the circumferential groove, the reinforcing element is located in the tread with a gradually decreasing axial width. The thickness extends radially over part or all of the height from the radially outer surface of the base layer towards the outer side of the tread, and the tread pattern elements arranged axially inward with respect to the first circumferential groove do not have A reinforcing element is provided adjacent to the axially inner face of the first circumferential groove, and the stiffness of the bottom layer is less than or equal to the stiffness of the rubber compound of the circumferential reinforcing element.

Viewed in a meridian section, the circumferential reinforcing elements have the shape of corners, the inflection points of which are oriented radially towards the outside, and are therefore arranged on the trailing edge of the rib or on the trailing edge of the most loaded tread pattern element on the outside of the tread of the tire, at The tread of the tire resists shear and vibration of these tread pattern elements during fast cornering due to its high compression and shear stiffness, thus making it possible to maintain a large area of contact with the running surface to limit the rib or tread element leading edge raised pressure on the rib, thereby limiting heat and rapid wear on the leading edge of the rib. The presence of reinforcing elements of this structure and a single groove has made it possible to obtain a significant improvement in the lateral grip properties of vehicle tires.

The circumferential reinforcing element also has the essential feature of being directly supported on the outer surface of the base layer. A slight decrease in the axial shear stiffness of the ribs was observed compared to bearing directly on the tire's crown reinforcement, but a significant increase in the tire's rolling resistance associated with easier lateral and longitudinal flattening of the tire's crown block.

Very advantageously, the tread pattern elements arranged axially inside the first circumferential groove do not have reinforcing elements arranged close to the axially inner face of this groove. This is because the presence of these reinforcing elements on the leading edge of the second rib of the tread tends to lead to a deterioration of the grip properties of the tire as well as the vehicle due to the high stiffness of the material of these reinforcing elements when they are in contact with the running surface .

It should also be noted that the reduction in the volume of the very hard rubber results in a significant reduction in the rolling resistance of the tire relative to the tire disclosed in the aforementioned document EP 2 708 382 A1.

Preferably, the circumferential reinforcement has two reinforcement elements, which are respectively arranged on the outer side adjacent to the first circumferential groove and the second circumferential groove of the tread from the outer side to the inner side and axially close to all the in the tread pattern elements of the first circumferential groove and the second circumferential groove.

This enhances the advantageous effect in terms of grip.

Advantageously, the tread has at least three circumferential grooves, and the circumferential reinforcement also has a further reinforcing element arranged on the outside adjacent to the third circumferential groove from the outside to the inside of the tread and in the axial direction in the tread pattern elements adjacent to said third circumferential groove.

The circumferential reinforcement can also advantageously have reinforcing elements arranged in all the tread pattern elements which are laterally adjacent to the circumferential groove and axially close to said circumferential groove.

According to an advantageous embodiment, the circumferential reinforcement has inner reinforcement elements arranged in the tread pattern elements inwardly adjacent to the circumferential groove which is axially closest to the inner side of the tire.

This makes it possible to stabilize the ribs or tread pattern elements on the inside of the tire when the inside is loaded as the leading edge when cornering. Thus, the same anti-vibration and anti-shear effects associated with the high compressive stiffness of the reinforcing element are found.

According to an advantageous exemplary embodiment, the tread has at least four circumferential grooves, the circumferential reinforcement has two inner reinforcing elements, each of which is arranged on the inner side adjacent to the tread from the inner side to the outer side. The first circumferential groove and the second circumferential groove are in and axially adjacent to the tread pattern elements of the first and second circumferential grooves.

According to another advantageous embodiment, the circumferential reinforcing elements are arranged symmetrically with respect to the median plane of the tire.

According to a particular exemplary embodiment, the tread has a circumferential groove through which the median plane passes, and two circumferential reinforcing elements are arranged axially close to and on either side of the circumferential groove through which the median plane passes.

The shape of the circumferential reinforcing element has a cross section tapered radially towards the outside. This increases its effectiveness as a support point. The walls of the circumferential reinforcing element can be concave, convex or stepped.

Preferably, the angle of the two side walls of the circumferential reinforcing element is between 35 and 45 degrees.

Below 35 degrees the effectiveness of the bearing points is reduced, while above 45 degrees the volume of the circumferential reinforcing elements becomes excessive.

According to a preferred embodiment, the reinforcing element has a base in radial contact with the outer surface of the base layer and a top extending radially towards the outside to at least half the height of the sides of the adjacent circumferential grooves.

This minimum height of the tops of the circumferential reinforcing elements is useful to obtain a stabilizing effect over the life of the tire.

According to an advantageous embodiment, the tops of the reinforcing elements at least partially form the sides of the adjacent circumferential grooves.

According to another advantageous embodiment, the tops of the reinforcing elements are arranged at an axial distance of 1 to 8 mm, preferably 2 to 5 mm, from the flanks of the adjacent circumferential grooves.

This embodiment makes it possible to maintain the remarkable effect of improving the lateral grip properties of vehicle tires without disrupting the molding of the tread circumferential grooves.

The base of the reinforcing element may advantageously extend axially below at least some bottoms of adjacent circumferential grooves.

This embodiment has the advantage of enhancing the effectiveness of the circumferential reinforcing elements.

According to another exemplary embodiment, the base of the reinforcing element extends axially below the tread pattern element on the side opposite the adjacent circumferential groove.

As previously mentioned, this has the advantage of stabilizing the circumferential reinforcing elements.

According to another advantageous exemplary embodiment, the base of the reinforcing element may be axially continuous and extend axially over at least 50% of the axial width of the tire tread.

Very advantageously, the base of the axially continuous reinforcing element extends axially over at most the axial width of the crown reinforcement. This makes it possible to maintain a good flattening of both shoulders of the tire and to limit the effect of the use of very high stiffness rubber compounds on the rolling resistance of the tire.

Advantageously, the rubber compound from which the circumferential reinforcement is made has a dynamic shear modulus G* greater than 20 MPa, preferably greater than 30 MPa, at 60° C., 10 Hz and an alternating shear stress of 0.7 MPa measured below.

Very advantageously, the rubber compound of the tread has a dynamic shear modulus G* of less than or equal to 1.3 MPa, preferably less than 1.1 MPa, said dynamic shear modulus G* at 60° C., 10 Hz and alternating shear of 0.7 MPa measured under shear stress.

The presence of circumferential reinforcements makes it possible to take full advantage of the gripping capabilities of this very low stiffness tread rubber compound. This is particularly useful in the case of tires for passenger vehicles.

According to an alternative embodiment, the base layer is interrupted axially under at least one circumferential groove of the tread. This makes it possible to obtain axial shear stiffness without sacrificing the ease of planarization of the rigid substrate.

The invention more particularly relates to motor vehicles intended to be fitted with three or more wheels, motor vehicles of the passenger vehicle type, SUVs ("Sport Utility Vehicles"), such as selected from the group consisting of lorries, heavy vehicles (ie subways, Buses, heavy road transport vehicles (trucks, tractors, trailers) or off-road vehicles) industrial vehicles, such as heavy agricultural vehicles or civil engineering vehicles, other transport or handling vehicles and two-wheeled vehicles (especially motorcycles), or aircraft tire.

Description of drawings

The subject matter of the present invention will now be described with the aid of the accompanying drawings, in which:

- Figure 1 shows very schematically (not drawn to any particular scale) a meridian cross-section through a tire according to an embodiment of the invention;

- Figures 2 to 11 depict the tread in a radial cross section of a tyre according to various embodiments of the invention; and

- Figure 12 shows an embodiment of the test tread in a meridian cross section.

Detailed ways

Figure 1 schematically shows a radial cross-section of a pneumatic tire or tire comprising a circumferential reinforcement 20 according to one embodiment of the present invention.

The tire 1 has an outside E and an inside I, the outside E is intended to be positioned towards the outside of the vehicle and the inside I is intended to be positioned towards the inside of the vehicle. Therefore, the tire exhibits tread asymmetry.

Figure 1 also shows the axial X, circumferential C and radial Z directions and the median plane EP (the plane perpendicular to the axis of rotation of the tire, which is located midway between the two beads 4 and through the crown reinforcement 6 in the middle).

The tire 1 has a crown 2 reinforced by a crown reinforcement or belt 6 , two sidewalls 3 and two beads 4 , each of these beads 4 being reinforced with bead wires 5 . The crown reinforcement 6 is covered by a rubber tread 9 located radially outside. A rubber underlayer 15 is located between the crown reinforcement and the tread. A carcass reinforcement 7 is wound around the two bead wires 5 in each bead 4 , the bead 8 of this reinforcement 7 being arranged, for example, towards the outside of the tire 1 . In a manner known per se, the carcass reinforcement 7 consists of at least one ply reinforced by so-called "radial" cords (eg fabric or metal), ie these cords are arranged substantially parallel to each other and extend from one tire to another. The bead extends to the other bead forming an angle between 80° and 90° with the intermediate circumferential plane EP. The inner liner 10 extends radially from one bead to the other on the inner side relative to the carcass reinforcement 7 .

Depending on the tire designer's purposes, this base layer 15 compound may have low hysteresis and low stiffness and thus improve the rolling resistance of the tire or be stiffer than the rubber compound forming the tread 9; in the latter case, the base layer has increased Effect of Shear Stiffness of Tire Tread. However, the stiffness of this bottom layer 15 is still less than the stiffness of the rubber compound of the circumferential reinforcement. In a particular embodiment, which simplifies the industrial production of tires according to the invention, the rubber compound of the base layer and the constituent rubber compound of the tread are the same.

The tread 9 has four grooves 11 , 12 , 13 and 14 from the outer side E to the inner side I. Each groove has an outer face 11.1, 12.1, 13.1 and 14.1, a groove bottom 11.2, 12.2, 13.2 and 14.2 and an inner face 11.3, 12.3, 13.3 and 14.3.

This tread 9 also has a circumferential reinforcement 20 constituted by reinforcing elements 22 arranged adjacent to the outer wall 12 . 1 of the second groove 12 . This reinforcing element 20 rests directly on the radially outer wall of the bottom layer 15 and has a substantially triangular cross-section. In the embodiment shown, the reinforcing element partially forms the outer wall 12 . 1 of the groove 12 .

The circumferential reinforcement 20 resists vibration and shear of the ribs adjacent to the outside of the groove 12 when the tire is heavily laterally loaded, oriented axially from the outside to the inside, for example, in a vehicle on which the tire is mounted with During a turn in the inside direction of the tire.

Figures 2 to 10 depict radial cross-sections of treads according to various embodiments of the present invention in the case of a tread pattern with three circumferential grooves.

The tread 30 in FIG. 2 has three grooves 11 , 12 and 13 and a circumferential reinforcement 32 comprising two circumferential reinforcement elements 34 and 36 . The circumferential reinforcing element 34 is arranged as in FIG. 1 , adjacent to the outer wall 12 . 1 of the second groove 12 . This circumferential reinforcing element 34 rests on the radially outer wall of the bottom layer 15 and forms in part the outer wall 12 . 1 of the groove 12 .

Additional circumferential reinforcing elements 36 are arranged adjacent to the outer wall 11 . 1 of the first groove 11 . By the presence of the additional circumferential reinforcing elements 36 , which counteract shearing and vibrations of the tread pattern elements adjacent to the outside of the first groove 11 , thus cooperating with the action of the circumferential reinforcing elements 34 when the tire is heavily laterally loaded. The tread has a rubber underlayer 15 , on one side in direct contact with the outer surface of the crown reinforcement 6 and on the other side in direct contact with the tread 9 and the base of the reinforcing elements 34 and 36 .

The circumferential reinforcement 42 of the tread 40 in FIG. 3 includes three circumferential reinforcement elements 44 , 46 and 48 . An additional circumferential reinforcement element 48 relative to the circumferential reinforcement 32 of FIG. 2 is provided adjacent to the outer wall 13.1 of the third groove. The three circumferential reinforcing elements of this tread 40 cooperate to oppose vibration and shearing of the tread pattern elements adjacent to the outside of the three grooves when lateral loads directed from the outside to the inside are strong. As mentioned above, the rubber base layer 15 is arranged between the crown reinforcement 6 and the tread 9 and the three circumferential reinforcing elements.

FIG. 4 shows an embodiment of a tread 50 according to one subject of the present invention, wherein, as shown in FIG. 3 , a circumferential reinforcement 52 includes three elements 54 , 56 and 58 and an additional circumferential reinforcement element 59 . This circumferential reinforcing element 59 is arranged adjacent to the inner wall 13 . 3 of the groove 13 . This circumferential reinforcing element 59 opposes vibrations and shearing of the tread pattern elements adjacent to the interior of the third groove 13 during the orientation of the lateral load from the inside to the outside. In this case, taking into account the dynamics of the vehicle when cornering, the loads directed from the inside to the outside are significantly weaker than those directed in the other direction, and there is no need to add additional circumferential reinforcing elements. In a bend at the limit of grip, the tires on the vehicle placed within the bend are heavily unloaded, taking into account the dynamics of the vehicle when cornering. However, this tire on the inside of the curve contributes to lateral grip by its facing the front shoulder of the vehicle. The presence of reinforcements on the asymmetric tires makes it possible to increase the total thrust on the axle due to the thrust of the two tires on the same axle. The bases of the four circumferential reinforcing elements bear directly on the radially outer surface of the bottom layer 15 .

In FIG. 5 , the tread 60 includes a circumferential reinforcement 62 consisting of four circumferential reinforcement elements 64 , 66 , 68 and 69 arranged in a similar manner to FIG. 4 . The four circumferential reinforcing elements have a base 61 and a top 63 . In the embodiment shown, the base 61, which is in direct contact with the outer surface of the base layer 15, extends below the ribs or tread pattern elements adjacent to the three grooves. These extensions enhance the reinforcement provided by the different circumferential reinforcement elements.

In FIG. 6 , the tread 70 includes a circumferential reinforcement 72 , which, as shown in FIG. 5 , consists of four circumferential reinforcement elements 74 , 76 , 78 and 79 . These circumferential reinforcing elements have tops 73 and bases 71 such that their bases 71 extend below the adjacent grooves. As previously mentioned, the base is in direct contact with the bottom layer 15 and reinforces the reinforcement provided by the various circumferential reinforcement elements. The radial height of the bases 71 is substantially equal to the radial position of the groove bottoms, so that they form the bottoms of the ribs. According to an alternative embodiment, the bottom of the rib is formed only by the compound of the tread.

In Figure 7, the tread 80 has a circumferential reinforcement 82 consisting of four circumferential reinforcement elements 84, 86, 88 and 89 such that its base 81 is axially continuous and extends from one side of the tread Continue to the other side. Thus, the base 81 is in continuous direct contact with the radially outer surface of the rubber underlayer 15 and has a significant effect of reinforcing the entire crown 2 of the tire. The tops 83 of the reinforcing elements partially form the sides of the adjacent ribs.

The axial width of the axially continuous base 81 covers at least half the axial width of the tread and at most the axial width W of the crown reinforcement 6 . The fact that the base is continuous increases the resistance of the entire crown block 2 to vibrations during lateral loads and the fact that they do not exceed the axial width of the crown reinforcement 6 promotes the flattening of the shoulders and limits the rolling resistance of the tire.

The depicted shape of the circumferential reinforcing elements is triangular, but in particular the shape may vary without departing from the scope of the invention, and the side walls may be concave, convex or stepped.

In the depicted embodiment, the angle a formed by the two side walls is approximately 40 degrees, ie between 35 and 45 degrees.

When the tire is new, the radial height of the circumferential reinforcing elements can reach the contact surface of the tread pattern elements, but can also be smaller. It should not be less than half the height of the tread pattern element in order to be able to function throughout the life of the tire.

FIG. 8 depicts a tread 90 whose circumferential reinforcement 92 consists of four circumferential reinforcement elements 94 , 96 , 98 and 99 as shown in FIG. 4 . Four circumferential reinforcing elements bear against the radially outer surface of the rubber base 95 . However, in this exemplary embodiment, bottom layer 95 is interrupted axially below the bottoms of grooves 11 , 12 and 13 . Thus, the bottom layer 95 consists of four circumferential strips. This embodiment has the advantage of not limiting lateral flattening when the stiffness of the base layer 95 is greater than the stiffness of the tread.

Circumferential reinforcing elements should serve as bearing points for counteracting shear and vibration of the tread pattern elements containing them. For this purpose, the mixture from which these circumferential reinforcing elements are made is preferably very significantly harder than the mixture of the tread 9 . Preferably, the dynamic shear modulus G* measured at 60° C., 10 Hz and 0.7 MPa alternating shear stress is greater than 20 MPa, very preferably greater than 30 MPa.

Such mixtures are described in particular in the applicant's application WO 2011/045342 A1.

An example of such a formulation is given in Table 1 below

Table 1

component C.1 NR(1) 100 Carbon Black(2) 70 Phenol-formaldehyde resin(3) 12 ZnO(4) 3 Stearic Acid (5) 2 6PPD(6) 2.5 HMT(7) 4 sulfur 3 CBS(8) 2

(1) Natural rubber;

(2) carbon black N326 (designated according to standard ASTM D-1765); (3) phenol-formaldehyde novolak resin ("Peracit 4536K" from Perstorp);

(4) Zinc oxide (industrial grade-Umicore);

(5) Stearin ("Pristerene 4931" from Uniqema);

(6) N-(1,3-Dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys);

(7) Hexamethylenetetramine (from Degussa);

(8) N-Cyclohexylphenylthiazole sulfenamide (Santocure CBS from Flexsys).

In particular through the combined action of epoxy resins and amine-containing curing agents, the formulation makes it possible to obtain mixtures of high stiffness. The shear modulus G* measured at 0.7 MPa alternating shear stress, 10 Hz and 60 °C was 30.3 MPa.

This very hard material for circumferential reinforcements is preferably used for low stiffness treads with a dynamic modulus G* of less than 1.3 MPa and preferably less than or equal to 1.1 MPa.

An example of a suitable formulation is given in Table 2 below:

Table 2

combination B1 SBR(a) 100 Silica (b) 110 Coupling agent (c) 9 Liquid Plasticizer (d) 20 Resin plasticizer (e) 50 carbon black 5 Zinc oxide 3 Stearic acid 2 Antioxidant (f) 2 Accelerator (g) 2 DPG 2 sulfur 1

Recipes are given by weight.

(a) SBR with 27% styrene, 1,2-butadiene: 5%, cis-1,4:15%, trans-1,4:80% Tg-48°C;

(b) "Zeosil 1165MP" silica from Solvay with a BET surface area of 160 m ² /g;

(c) "SI69" TESPT silane from Evonik;

(d) "Flexon 630" TDAE oil from Shell;

(e) "Escorez 2173" resin from Exxon;

(f) Antioxidant "Santoflex 6PPD" from Solutia;

(g) Accelerator "Santocure CBS" from Solutia.

The dynamic shear modulus after vulcanization was 0.9 MPa.

FIG. 9 depicts a tread 100 having a circumferential reinforcement 102 having three circumferential reinforcement elements 104 , 106 and 108 arranged in FIG. 3 , the three circumferential reinforcement elements 104 , 106 and 108 bear directly on the bottom layer 15, close to the three grooves and on the outside. However, in this embodiment, the inner side walls of the tops 103 of the three circumferential reinforcing elements do not form part of the outer surfaces of the ribs, but are offset axially towards the outside so as to be 1 to 8 mm from the outer surfaces of these ribs, Preferably, they are spaced apart by a distance of 2 to 5 mm. This offset makes it possible not to disrupt the moulding of the ribs during vulcanization of the tire without reducing the effectiveness of the circumferential reinforcing elements.

In this Figure 9 it can also be seen that the tops of the circumferential reinforcing elements 104 extend radially up to the outer surface of the tread pattern elements. This allows electrostatic charges to be released more easily due to the conductive properties of the mixture of circumferential reinforcing elements.

Figures 10 and 11 depict another embodiment of a tire according to the present subject matter in which circumferential reinforcements are arranged symmetrically in the tread.

The tread 120 of FIG. 10 has three grooves 11 , 12 and 13 and a circumferential reinforcement 122 . In this embodiment according to one subject of the present invention, the circumferential reinforcement 122 comprises four circumferential reinforcement elements 124, 126, 128 and 129, which are relative to the The median plane EP is arranged symmetrically and bears directly on the surface of the bottom layer 15 . The arrangement of the three circumferential reinforcement elements 124 , 126 and 128 is similar to reinforcement elements 54 , 56 and 59 in FIG. 4 . In contrast, the reinforcing element 129 is arranged axially on the inner side relative to the groove 12, thus forming at least part of the inner surface 12.3 of this groove. Thus, the circumferential reinforcement 122 does not add any asymmetry to the tread 120, making it easier to install when such a tire does not have any other asymmetry. Therefore, the outside of such a tire can be mounted towards the outside or inside of the vehicle, which in this case are only geometrical references.

FIG. 11 depicts a tread 130 with four grooves 11 , 12 , 13 , 14 and circumferential reinforcements 132 . The circumferential reinforcement 132 has four circumferential reinforcement elements 134 , 136 , 138 and 139 abutting against the surface of the base layer 15 . In the embodiment of Figure 12, these four circumferential reinforcing elements are arranged symmetrically with respect to the median plane EP of the tire. Reinforcing elements 134 and 136 are respectively arranged on the outside of groove 12 and groove 11 in the axial direction; reinforcing elements 138 and 139 are respectively arranged on the inner side of groove 14 and groove 13 in the axial direction.

Specifically for asymmetric or symmetrical tires, one skilled in the art as a tire designer should be able to adjust the number and location of circumferential reinforcing elements to obtain optimal resistance to vibration and shear of the ribs and tread pattern elements.

test

The rubber compound was characterized as follows.

Dynamic properties are well known to those skilled in the art. These properties were measured on a viscosity analyzer (Metravib VA4000) using test samples moulded from the unvulcanized mixture or bonded to the vulcanized mixture. The test samples used were those described in Figure X2.1 (Circle Ring Test Sample) in standard ASTM D 5992-96 (using the September 2006 edition first adopted in 1996). The diameter "d" of the test sample is 10mm (hence the circular section is 78.5mm ² ) and the thickness "L" of each part of the mixture is 2mm, which gives a ratio "d/L" of 5 (contrary to standard ISO 2856, As mentioned in paragraph X2.4 of the ASTM standard, the recommended value of d/L is 2).

The response of a sample of the cured composition subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz was recorded. The maximum shear stress applied was 0.7 MPa.

Measurements were performed at a minimum temperature below the glass transition temperature (Tg) of the mixture or rubber to a maximum temperature greater than 100°C with a temperature change of 1.5°C/min. The test samples were acclimated to the lowest temperature for 20 minutes prior to the start of the test to ensure good temperature uniformity among the test samples.

The results used are in particular the values of the dynamic shear modulus G* at a temperature of 60°C.

The performance of tires according to the subject of the present invention was measured during the following tests:

- Longitudinal braking distance: measures the distance required to go from 80km/h to 20km/h on wet ground.

- Steering stiffness: For a given drift angle, the axial lateral thrust of the tire is measured during rolling.

- Speed test on the Charade circuit: The test consists of four laps and the performance chosen is the average of the four times. Tests were performed with control tires at the beginning and end of the test, so that possible drifts associated with changes in conditions such as air temperature and ground temperature could be corrected.

test

Figure 12 depicts very schematically a cross-section of the tread of a tire used for vehicle testing.

The tread 110 has four grooves 11 , 12 , 13 and 14 . The two compounds make up the tread, with compound 113 radially outside of bottom layer 115 . Said tread 110 also has a circumferential reinforcement 112 comprising five circumferential reinforcement elements 114 , 116 , 117 , 118 and 119 which rest radially directly against the outer surface of the base layer 115 . Circumferential reinforcing elements 114, 116 and 118 are each disposed adjacent to the outer surface of one of the three outermost ribs. The circumferential reinforcing elements 119 and 120 are themselves arranged adjacent to the inner surface of one of the two ribs arranged closest to the inside. Thus, the third rib is reinforced by two circumferential reinforcing elements. Each circumferential reinforcing element has a substantially triangular shape and is intended to be in direct contact with the radially outer surface of the rubber base 115 and one of its side walls partially forms the side of the rib.

The tread 110 of the test tire was produced by a profile with two mixtures made of the tread 113 and the base layer 115, obtained by co-extrusion. The profile has four grooves. Profiles of the same length corresponding to the four circumferential reinforcing elements are also produced by extrusion. Then, from the co-extruded profile of the two tread compounds with the heated chisel, four compound volumes, each corresponding to the volume and shape of the circumferential reinforcing elements, were removed, and the four circumferential reinforcing elements were manually placed on the This is produced in four volumes. The tread thus assembled is then placed on the crown of the tire in a manner known to those skilled in the art to complete it. The complete tire is then vulcanized as usual in a vulcanizer.

The reference tires are Pilot Sport 3 Michelin tires, size 225/45R17, with a front pressure of 2.3 bar and a rear pressure of 2.7 bar, and the test vehicle is a Renault Clio Cup.

These reference tires R1 have treads whose mixtures have a dynamic shear modulus G* at 60° C. of 1.4 MPa.

Another reference tire, the R2, was also produced. The tread of these tires is identical to that of Figure 12, except that the four circumferential reinforcing elements and the base layer are absent. These tires have a tread pattern formed by only the four circumferential grooves shown.

The tread compound of the reference tire R2 had a G* value of 0.9 MPa at 60°C.

The test tire E1 had a tread compound with a G* value of 0.9 MPa, and the circumferential reinforcing elements were made of a compound with a G* value of 30 MPa. These tires E1 have circumferential reinforcements corresponding to FIG. 10 , but without a bottom layer.

The other tire E2 according to the invention was produced with a tread and circumferential reinforcements like E1, but additionally with a base layer. Preferably, the mixture from which the bottom layer is prepared has a dynamic shear modulus G* of less than 20 MPa, preferably less than 10 MPa, measured at 60°C, 10 Hz and an alternating shear stress of 0.7 MPa. In tire E2, the dynamic shear modulus G* of the base compound is equal to 5 MPa. The bottom layer is continuous as shown in FIG. 12 . The thickness of this base layer in the tread pattern is about 2 mm.

The circumferential reinforcing elements have an angle of 40 degrees between their side walls.

table 3

Using a lower stiffness tread generally reduces the steering stiffness of the tire and improves braking performance on wet surfaces.

The tires tested according to the invention made it possible to obtain a braking performance gain of 10 points on wet surfaces, while having a steering stiffness comparable to that of the control R1.

Table 4

time time gain R1 2min 18s - R2 2min 17.7 0.3s E1 2min 17.2 0.8s E2 2min 17.0 1.0s

The gain from 0.3s on this track is considered significant.

It can be seen that the use of a tread with a very low stiffness compound yields only barely significant gains, whereas the results obtained with the tire with circumferential reinforcements according to the invention are very significant.

Thus, the presence of circumferential reinforcements in the tread makes it possible to fully exploit the potential grip of lower stiffness tread compounds.

By combining the choice of tread compound, the choice of the mix of base layer and circumferential reinforcement, tire designers can compensate for the tradeoffs between grip and behavior and rolling resistance, respectively, that cannot be achieved by selecting a single tread material.

Claims (10)

1. Tyre (1) having an axis of rotation and a median plane (EP) perpendicular to the axis of rotation, and comprising a crown having:

a crown reinforcement (6); and

a tread (9, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130) located radially on the outside, the tread comprising:

a plurality of tread pattern elements having lateral faces (11.1, 11.3, 12.1, 12.3, 13.1, 13.3, 14.1, 14.3) and a contact face intended to be in contact with the road surface when the tyre is driven;

a plurality of circumferential grooves (11, 12, 13, 14), each circumferential groove being delimited by an outer side (11.1, 12.1, 13.1, 14.1) and an inner side (11.3, 12.3, 13.3, 14.3) of opposite adjacent tread pattern elements, and by a bottom (11.2, 12.2, 13.2, 14.2);

o circumferential reinforcement (20, 32, 42, 52, 62, 72, 82, 92, 102, 112, 122, 132) made of a rubber compound having a stiffness greater than that of the rubber compound of the rest of the tread; and

an underlayer (15, 95, 115) arranged radially towards the inside and radially outside the crown reinforcement;

characterized in that the tyre has an outer side (E) and an inner side (I), the circumferential reinforcement having reinforcing elements (22, 34, 36, 44, 46, 54, 56, 64, 66, 74, 76, 84, 86, 94, 96, 104, 106, 114, 116, 124, 126, 134, 136) provided in tread pattern elements arranged axially on the outer side with respect to one of a first and a second circumferential groove of the tread from the outer side to the inner side and axially close to said circumferential groove, the reinforcing elements extending radially from the radially outer surface of the underlayer towards the outer side of the tread over part or all of the height of the tread thickness with a progressively decreasing axial width, the tread pattern elements arranged axially on the inner side with respect to the first circumferential groove (11) not having reinforcing elements provided close to the axially inner face of the first circumferential groove, and the stiffness of the bottom layer is less than or equal to the stiffness of the rubber compound of the circumferential reinforcement.

2. Tyre according to claim 1, wherein the circumferential reinforcement (32, 42, 52, 62, 72, 82, 92, 102, 112, 122, 132) has two reinforcing elements respectively provided in tread pattern elements adjacent to the outer side in a first circumferential groove (11) and a second circumferential groove (12) from the outer side to the inner side of the tread and axially adjacent to said first circumferential groove (11) and second circumferential groove (12).

3. Tyre according to claim 1, wherein said tread has at least three circumferential grooves (11, 12, 13), the circumferential reinforcement (42, 52, 62, 72, 82, 92, 102, 112) further having another reinforcing element provided in a tread pattern element adjacent to and axially adjacent to a third circumferential groove (13) of the tread from the outside to the inside.

4. Tyre according to claim 1, wherein the circumferential reinforcement (42, 52, 62, 72, 82, 92, 102) has reinforcing elements provided in all tread pattern elements adjacent to and axially close to the circumferential groove on the outer side.

5. Tyre according to claim 1, wherein the circumferential reinforcement (52, 62, 72, 82, 92, 112, 122, 132) further has an inner reinforcing element provided in the tread pattern element adjacent, on the inner side, to the circumferential groove axially closest to the inner side of the tyre.

6. Tyre according to claim 5, wherein the tread (110, 130) has at least four circumferential grooves, the circumferential reinforcement (112, 132) having two inner reinforcing elements respectively provided in tread pattern elements adjacent to and axially adjacent to the first and second circumferential grooves of the tread from the inner side to the outer side.

7. Tyre according to claim 1, wherein the circumferential reinforcing elements (124, 126, 128, 129, 134, 136, 138, 139) of the circumferential reinforcement (122, 132) are arranged symmetrically with respect to said median plane.

8. Tyre according to claim 7, wherein the tread has a circumferential groove crossed by a median plane, the two circumferential reinforcing elements (124, 129) being arranged axially close to and on either side of said circumferential groove crossed by said median plane.

9. Tyre according to claim 1, wherein the angle of the two sidewalls of the reinforcing element is between 35 and 45 degrees.

10. Tyre according to claim 1, wherein the reinforcing elements have a base (61, 71, 81) and a top (63, 73, 83, 103) radially arranged on the outer surface of the underlayer, said top extending radially towards the outside for at least half the height of the side of the adjacent circumferential groove.

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